Electrophysiology catheter design

ABSTRACT

A device and system for mapping and/or ablation wherein conductive portions of the electrodes and insulated portions of the electrode are composed of the same material. The system may generally include a medical device coupled to a console, the device including a distal assembly positionable at or near a target tissue region. The distal assembly may include one or more electrodes that include an integrated electrode head and electrode wire. The wire may be insulated by an oxidized layer. Alternatively, the distal assembly may include a plurality of protruding circumferential electrodes that are spaced apart by substantially insulated portions. The electrodes and insulated portions may be composed of the same material, with the insulated portions including an oxidized layer on an external surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims priority to U.S. ProvisionalPatent Application Ser. No. 61684385, filed Aug. 17, 2012, entitledMONOPHASIC ACTION POTENTIAL CATHETER DESIGN, and is related to andclaims priority to U.S. Provisional Patent Application Ser. No.61727163, filed Nov. 16, 2012, entitled MONO-PHASIC ACTION POTENTIALELECTROGRAM CATHETER, the entirety of both of which is incorporatedherein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

n/a

FIELD OF THE INVENTION

The present invention relates to a device and system for improvedmapping and tissue ablation that may be manufactured at a reduced costand complexity.

BACKGROUND OF THE INVENTION

Medical procedures are available for treatment of a variety ofcardiovascular conditions, such as cardiac arrhythmias, atrialfibrillation, and other irregularities in the transmission of electricalimpulses through the heart. As an alternative to open-heart surgery,many medical procedures are performed using minimally invasive surgicaltechniques, where one or more slender implements are inserted throughone or more small incisions into a patient's body. Such procedures mayinvolve the use of catheters or probes having multiple sensors,electrodes, or other measurement and treatment components to treat thediseased area of the heart, vasculature, or other tissue.Minimally-invasive devices are desirable for various medical andsurgical applications because they allow for shorter patient recoverytimes compared to surgery, and for precise treatment of localizeddiscrete tissues that are otherwise difficult to access. For example,catheters may be easily inserted and navigated through the blood vesselsand arteries, allowing non-invasive access to areas of the body withrelatively little trauma, while other minimally-invasive probes orinstruments may be inserted into small openings and directed throughtargeted anatomy without significant impact or disruption to surroundingtissue.

One such example of a minimally invasive therapy involves the treatmentof cardiac arrhythmias or irregular heartbeats in which physiciansemploy specialized cardiac assessment and treatment devices, such as amapping and/or ablation catheter, to gain access to interior regions ofa patient's body. Such devices may include tip electrodes or otherablating elements to create lesions or other anatomical effects thatdisrupt or block electrical pathways through the targeted tissue. In thetreatment of cardiac arrhythmias, a specific area of cardiac tissuehaving aberrant electrical activity (e.g. focal trigger, slowconduction, excessively rapid repolarization, fractionated electrogram,etc.) is typically identified first before subsequent treatment. Thislocalization or identification can include obtaining monophasic actionpotential (“MAP”) electrograms of a particular cardiac region.Monophasic action potential recordings document the onset of localtissue depolarization, during repolarization, and the general actionpotential morphology. The MAP signal is generated by measurement betweentwo electrodes, the first being in contact with the blood but generallynot in contact with the myocardium, and the second being in contact withthe myocardium, with high enough local pressure to depolarize theunderlying myocytes. This increased local pressure preferably is createdby a relatively prominent, yet small surface area electrode in stablecontact with the myocardium.

MAP signals may be obtained by temporarily depolarizing selected tissue,with responsive electrical activity being recorded or otherwisemonitored for an indication of local depolarization timing, refractoryperiod duration, and any aberrant electrical activity. After mapping anddiagnosing aberrant tissue, a physician may decide to treat the patientby ablating the tissue. Accurate mapping of the cardiac tissue canreduce the number of ablations necessary to treat an aberrant electricalpathway, and can make the executed ablations more effective. Inaddition, MAP recordings can aid in the determination of the timing oflocal tissue activation which is often ambiguous when recorded usingstandard intracardiac electrodes.

The accuracy of MAP signal measurement largely depends on quality ofcontact between one or more mapping electrodes and the heart tissue. Forexample, motion artifacts caused by a beating heart and nonuniformventricular contraction can significantly distort detected MAP signals,as movement of the heart will vary the pressure of (and therefore alterthe contact between) the mapping electrodes on the heart tissue as wellas resulting in unstable sliding contact of the electrodes. Currentlyknown diagnostic cardiac electrophysiology catheters do not accuratelyand reliably detect MAP signals.

Further, combination mapping and ablation devices reduce procedure timeand complexity by eliminating the need to employ separate mapping andablation devices for each task. Combination mapping and ablation devicesalso increase ablation accuracy, because once aberrant tissue (the“target tissue”) is found, ablation can begin immediately without havingto remove the mapping device and relocate the target tissue with theablation device. It is desirable to include one or more largerelectrodes for radiofrequency (RF) ablation, so the large electrode areacan provide a large surface area for dissipation into the blood pool ofheat absorbed from the tissues. When smaller electrodes, and therefore asmaller active surface area, are used, the electrodes are more likely toincur local overheating, which can lead to thermal denaturation of bloodproteins, producing adherent or embolic coagulum or other undesirableeffects downstream of the electrodes and the treatment site. Conversely,more accurate electrograms and MAP recordings may be obtained only withsmaller mapping electrodes.

To provide more effective and efficient medical treatments, it is thusdesirable to optimize the apparatus and method of use to ensure moreuniform contact between a mapping device and cardiac tissue whenrecording MAP signals. It is also desirable to have a catheter that canboth record monophasic action potentials, and subsequently ablate thelocal tissue if desired. It is further desirable to provide a mappingapparatus that is simple and cost effective to manufacture.

SUMMARY OF THE INVENTION

The present invention relates to a device and system wherein theconductive portions and nonconductive portions may be composed of thesame material. The device may generally include an elongate body havingan external surface, and a metal electrode having a proximal portion, adistal portion, and an external surface, at least a portion of theproximal portion of the electrode being disposed within the elongatebody and at least a portion of the distal portion of the electrode beingdisposed about the external surface of the elongate body. The electrodemay be composed of a metal such as gold, gold alloys, gold with acoating of tantalum, copper with a coating of tantalum, copper with acoating of gold, aluminum tungsten, titanium, tantalum, hafnium,niobium, zirconium, and mixtures thereof, for example, tantalum. Theportion of the electrode disposed within the elongate body may include asubstantially insulative layer, for example, a layer of oxidized metalsuch as aluminum, tungsten, titanium, tantalum, hafnium, niobium,zirconium, and alloys thereof. For example, the layer of oxidized metalmay be tantalum pentoxide. The distal portion of the electrode may becoiled about the external surface of at least a portion of the distalportion of the elongate body, and the coiled portion may include atleast two coils of approximately 360° each. Further, the electrode maybe a hypotube electrode having a lumen containing saline for cooling theelectrode during use.

In another embodiment, the device may generally include an elongate bodyhaving an external surface, a proximal portion, and a distal portion,and a plurality of electrodes composed of a tantalum and having aninsulated proximal portion, a conductive distal portion, and an externalsurface, at least a portion of the proximal portion of each of theplurality of electrodes being disposed within the elongate body andhaving an insulative oxidized layer, and a distal portion of each of theplurality of electrodes being coiled about the external surface of atleast a portion of the distal portion of the elongate body. For example,the plurality of electrodes may be hypotube electrodes.

In another embodiment, a device distal assembly may generally include adistal assembly housing element having a longitudinal axis and anexternal surface, the distal assembly housing element being composed ofa conductive material having a substantially insulative layer on theexternal surface, and a plurality of electrodes coupled to the distalassembly housing element, the plurality of electrodes being composed ofa conductive material and substantially having a radial symmetry aboutthe housing element longitudinal axis, each of the plurality ofelectrodes including an integrated electrode head and electrode wire,each electrode wire having an external surface and a substantiallyinsulative layer on the external surface. The conductive material may beselected from the group consisting of metals, doped semiconductors,conductive polymers, metal polymers, and metal-ceramic composites.Specifically, the conductive material may be a metal such as platinum,platinum alloys, gold, gold alloys, gold with a coating of tantalum,copper, copper with a coating of tantalum, copper with a coating ofgold, aluminum, tungsten, titanium, tantalum, hafnium, niobium,zirconium, and combinations thereof. The substantially insulative layermay be pyrolytic graphite, graphite, graphene, diamond, diamond-likecarbon (DLC) coating, alumina, sapphire, zirconia, tantala, titania,beryllium oxide, polymer composites containing thermally conductiveparticles, nanoparticles, self-assembling nanoparticles, nanomaterialsand composites, olive oil, medical grade silicone oil, or combinationsthereof. For example, the conductive material may be tantalum and thesubstantially insulative layer may be tantalum pentoxide.

The system may generally include a radiofrequency energy source, adistal assembly housing element having a longitudinal axis, the distalassembly housing element being composed of a conductive material andbeing in electrical communication with the radiofrequency energy source,and a plurality of electrodes coupled to the distal assembly housingelement and in electrical communication with the radiofrequency energysource, the plurality of electrodes being composed of a conductivematerial and substantially having a radial symmetry about the housingelement longitudinal axis, each of the plurality of electrodes includingan integrated electrode head and electrode wire, each electrode wirehaving an external surface and a substantially insulative layer on theexternal surface. Further, a substantially insulative layer may bedisposed between the distal assembly housing element and the pluralityof electrodes, such that the distal assembly housing element andplurality of electrodes are electrically isolated from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 shows a medical system including a catheter having a distalassembly;

FIG. 2 shows a first embodiment distal assembly;

FIG. 3 shows a bulbed wire of the distal assembly of FIG. 2;

FIG. 4 shows a schematic diagram of an electrochemical cell for use inconjunction with anodizing and annealing bulbed wires, such as forming atantalum pentoxide layer on a tantalum surface;

FIG. 5 shows a simplified depiction of a holder adapted to containbulbed wires for use in conjunction with a process for imparting furthercorrosion resistance or selective electrical conductivity to the bulbedwires of FIG. 2;

FIG. 6A shows a second embodiment of a distal assembly;

FIG. 6B shows a third embodiment of a distal assembly;

FIG. 7A shows a fourth embodiment of a distal assembly;

FIG. 7B shows a fifth embodiment of a distal assembly;

FIG. 8 shows a sixth embodiment of a distal assembly;

FIG. 9A shows a seventh embodiment of a distal assembly;

FIG. 9B shows an eighth embodiment of a distal assembly;

FIG. 9C shows a ninth embodiment of a distal assembly;

FIG. 10A-10H show various configurations of a tenth embodiment of adistal assembly;

FIG. 11 shows an eleventh embodiment of a distal assembly;

FIG. 12A shows a twelfth embodiment of a distal assembly; and

FIG. 12B shows a view of the anterior face of an embodiment of thedistal assembly of FIG. 12A.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “distal assembly” refers to a distal portion ofa medical device that has mapping and/or ablation functionality. If themedical device includes an elongate body, at least a portion of thedistal assembly may be distal of the elongate body (for example, asshown in FIGS. 9A-10), or the distal assembly may be substantiallyaffixed on, disposed about, or integral to the distal portion of themedical device (for example, as shown in FIGS. 2 and 6A-7B).

As used herein, the term “selectively conductive metal” refers to ametal with an oxide form or coating that behaves like a capacitor,passing high-frequency currents and pulsed energy but blockingtransmission of direct current and low-frequency signals. The metal, forexample, aluminum, tungsten, titanium, tantalum, hafnium, niobium,zirconium (and alloys thereof), as well as gold or copper with a thinfilm of tantalum, or copper with a thin film of gold, may be fullyelectrically conductive. The oxide of that metal, on the other hand, mayhave low resistance to high-frequency current flow, thus beingselectively conductive, and a high resistance to low-frequency or directcurrent flow, thus having selectively insulative properties.

Referring now to FIG. 1, a medical system 10 including a catheter 12having a distal assembly 14 is shown. The system 10 may generallyinclude a medical device 12 (such as a catheter or surgical probe)coupled to a console 16 or other operating equipment. The catheter 12has a distal assembly 14 positionable at or near a target tissue region.The catheter 12 may have an elongate body or catheter shaft 18 with aproximal portion 20, a distal portion 22, and may define a lumentherebetween (not shown in FIG. 1). The distal portion 22 of theelongate body 18 may include one or more reference electrodes 24 inelectrical communication with the distal assembly 14 and console 16. Theconsole 16 may include one or more computers 26 for storing data,interpreting signals received from the device (for example, determiningwhether received signals indicate an aberrant electrical activity withina patient's heart), generating alerts, controlling the system, and thelike, and may also include one or more fluid reservoirs 27, vacuums,power sources, and the like. The elongate body 18 may be both flexibleand resilient, with sufficient column strength and torsional rigidityfacilitating steady contact with tissue to improve signal fidelity inmapping contacted tissue. The catheter 12 may also have a handle 28affixed to the proximal portion 20 of the elongate body, which mayinclude one or more fluid inlet and outlet ports, actuators, connectors,and other control and/or connecting elements.

The distal assembly 14 is coupled to the distal portion 22 of theelongate body 18, and includes one or more mapping and/or ablationelectrodes 30, each comprising an electrode head 32 and electrode wire34. The one or more electrodes 30 may be permanently affixed to anelectrode assembly housing 36 (as shown and described in FIGS. 2-5). Thedistal assembly 14 may be operable at least for mapping a target tissueregion, but may also be operable as a treatment assembly. For example,the console 16 may include a radio frequency (RF) generator or highvoltage pulsed energy generator 38 in electrical communication with oneor more of the electrodes 30 or the electrode assembly housing 36 suchthat the distal assembly 14 may also be used to ablate or electroporatea target tissue region. The catheter 12 and system 10 may be configuredfor use with any of a variety of energy modalities, includingcryoablation, RF ablation, and electroporation. Further, the catheter 12and system 10 may be configured for mapping tissue, for example,recording and processing electrograms from cardiac tissue.

Referring generally to FIGS. 2-10, embodiments of the distal assembly 14and methods for manufacturing are shown and described. In allembodiments, the distal assembly 14 offers a cost effective and qualityperformance advantage over currently known devices. For example,although all embodiments may provide more accurate mapping, the distalassembly 14 of FIG. 2 may offer combined mapping and ablationfunctionality in a space-saving configuration with fewer components andmanufacturing steps, whereas the distal assemblies 14 of FIGS. 6A, 6B,and 8-10 may further offer the advantage of having combinedfunctionality without the need for creating each component from adifferent material. Further, the distal assembly 14 of FIGS. 8-10 mayoffer the advantage of including features that enhance contact betweenmapping electrodes and tissue. Finally, the distal assemblies 14 ofFIGS. 7A and 7B may offer the advantage of including a single electrodethat has both mapping and ablation functionality.

The distal assemblies 14 of FIGS. 2-10 may include components (forexample, mapping and/or electrodes and/or a housing assembly) that arecomposed of a selectively conductive material. Metal oxides such astantalum pentoxide may be referred to as “selectively conductivemetals.” Tantalum pentoxide, for example, is selectively conductive.That is, it has the unique ability to block direct current (DC) whileallowing high-frequency current conduction (such as radiofrequencyenergy). Tantalum pentoxide passes high-frequency current preferentiallybut blocks DC transmission. Metals such as tantalum, aluminum, tungsten,titanium, haffnium, niobium, zirconium, and mixtures thereof, which haveoxides that are selectively conductive. Additionally, dopedsemiconductors such as p-type and n-type doped silicon and gallium, andcomposite materials made from ceramics as well as conductive polymers,metal-polymers, metal-ceramic composites, and some nanomaterials mayalso be selectively conductive. Further, tantalum (Ta) and tantalumcompounds such as grain-stabilized tantalum (TaKS), tantalum pentoxide(Ta₂O₅), tantalum-tungsten (TaW), capacitor quality tantalum (TaK), orsimilar are highly corrosion resistant. Tantalum compounds also displayexcellent cold ductility, high melting point (for example, Ta has amelting point of 3,017° C.), outstanding resistance against aqueoussolutions and metal melts, superconductivity, and a high level ofbiocompatibility. Further, TaKS, for example, is radiopaque, making itwell suited for use in catheters that must be located within andnavigated through a patient's body. Tantalum and tantalum compounds canbe even more durable than MP35N (a nickel-cobalt-chromium-molybdenumalloy commonly used material for medical implantable devices such ascatheter wires that is nonmagnetic, has high tensile strength, goodductility and toughness, and excellent corrosion resistance) and is lessexpensive than platinum. Additionally, as shown in FIGS. 7A and 7B, thedistal assembly 14 may include a single electrode 30, wherein at least aportion of which is composed of a tantalum compound (for example, Ta₂O₅)and at least a portion of which is composed of a different material (forexample, gold, gold alloy, copper coated with gold, or platinum). As aresult, the tantalum portion of the electrode may be used to ablate orelectroporate tissue using, for example, RF energy (for example, renal,liver, or prostate tissue), whereas the non-tantalum portion of theelectrode may be used to deliver a direct current stimulus to or recorddirect current from the tissue.

Referring now to FIG. 2, a first embodiment of a distal assembly 14 isshown. The distal assembly 14 may include a housing 36 and one or moreelectrodes 30, such as monophasic action potential (MAP) electrodes,each positioned a radial distance from the longitudinal axis 40 of thehousing 36. If two electrodes 30 are used, the electrodes 30 may bepositioned opposite each other. If three or more electrodes 30 are used(for example, four electrodes are shown in FIG. 2), the electrodes 30may have a radial symmetry about the housing longitudinal axis 40.

The distal assembly 14 shown in FIG. 2 may have been formed according tothe method shown and described in FIGS. 3-5. For example, one or morebulbed wires 42 comprising a bulb portion 44 and a wire portion 46 maybe created (as shown and described in FIG. 3). The wire 46 portion ofeach bulbed wire 42 may then be anodized (as shown and described in FIG.4), and the bulb portion 44 of each bulbed wire 42 may be composed ofthe non-anodized material or be electroplated, sputtered, orion-embedded with a corrosion-resistant material or material havingother beneficial properties (as shown and described in FIG. 5).

Once one or more bulbed wires 42 have been treated (for example,anodized and electroplated), the wires 42 may be placed into and bondedto an electrode assembly housing (referred to as the “assembly housing”)36. For example, four bulbed wires 42 may be used. At this stage (thatis, when the bulbed wires 42 are seated within the mapping assemblyhousing 36), the bulbed wires are referred to as electrodes 30,comprising electrode heads 32 and electrode wires 34. In the embodimentshown in FIG. 2, the electrodes 30 and electrode assembly housing 36 arecollectively referred to as the distal assembly 14. However, not allembodiments include a housing 36 (for example, the embodiments of FIGS.6A, 6B, 9, and 10A-10C). The assembly housing 36 includes an anteriorface 48 from which the one or more electrode heads 32 may protrude.Alternatively, the electrode heads 32 may be mounted within the assemblyhousing 36 such that the electrode heads 32 are substantially flush withthe anterior face 48 of the electrode housing 36. For example, theassembly housing 36 may include a socket sized to receive each electrode30 such that the electrode head 32 is seated within the socket and theelectrode wire 34 passes through an opening in the socket and into theelongate body, once the housing is coupled to an elongate body. Theelectrodes 30 may be affixed to the electrode assembly housing 36 usingadhesive, thermoplastics, or other known techniques.

The distal assembly 14 of FIGS. 2-5 may be particularly suited fordiagnostic purposes, i.e. mapping. However, the distal assembly 14alternatively may be used as part of a combination ablation and mappingdevice 12. For example, the assembly housing 36 may be in electricalcommunication with an energy source (such as RF energy) and composed ofan electrically conductive material, or coated or cladded with anelectrically conductive material, so that the electrodes 30 may be usedfor mapping and the housing 36 (which may have a larger “footprint” thanthe mapping electrodes) may be used for ablation. In this case, a thininsulative layer could be incorporated to electrically isolate theelectrode heads 32 from the assembly housing 36. For example, aninsulative layer could be disposed within the sockets of the assemblyhousing 36. Alternatively, the assembly housing 36 and electrodes 30 maybe composed of a conductive material, but the housing 36 may include anouter layer of a selectively conductive material. Additionally oralternatively, the assembly housing 36 may be composed of alow-durometer, resilient material such as silicone, a polymer orconductive polymer, air-filled balloon, gel, fiber composite, or thelike, that conforms to irregular geometries while ensuring contactbetween the electrode head 32 and target tissue region. For example, asthe heart beats, the deformable housing may absorb the pressure topreserve contact between the electrode head and target tissue region.

Once assembled, the distal assembly 14 may be coupled to the distalportion 22 of the elongate body 18, with the electrode wires 34providing electrical connection between the distal assembly 14 andcatheter 12 and/or system 10. Thus, the entire distal assembly 14 mayinclude as little as two components (for example, if a single electrodeand distal assembly housing were used). In a non-limiting embodiment,the distal assembly 14 as shown in FIG. 2 may include six components:four electrodes 30, the assembly housing 36, and a reference electrode24. The assembly housing 36 and electrodes 30 may be composed of thesame material. This embodiment includes fewer components than knownmapping assemblies, at least in the electrodes, which reduces cost andassembly time while providing higher reliability.

Referring now to FIG. 3, a bulbed wire 42 of the distal assembly 14 ofFIG. 2 is shown. The bulbed wire 42 may be manufactured or molded from avolume of metal such that a bulb 44 or substantially spherical shape isformed at one end (referred to as the “bulb”), such as by cold formingand/or extrusion. The bulb 44 may become the electrode head 32 (as shownand described in, for example, FIGS. 2, 4 and 5), so it may have anydimensions suitable for the final mapping assembly. Having asingle-piece electrode head 32 and electrode wire 34 eliminates the needto weld an electrode to a wire. A two-piece system is also feasible, butwould increase cost and manufacture time and complexity. The bulbed wire42 may be composed of a highly corrosion-resistant material, such astantalum or tantalum compound (such as Ta₂O₅ or TaKS).

Referring now to FIG. 4, a schematic diagram of an electrochemical cell50 for use in conjunction with anodizing and annealing bulbed wires 42is shown. Once the bulbed wire 42 of FIG. 3 is formed, the wire portion46 may be anodized to create a thin oxide layer on the external surfaceof the wire portion 46. For example, the insulating layer may beapproximately 1 μm thick. During the anodizing process, the wire portion46 is placed into a container 52 containing an electrolytic solution 54such as H₃PO₄, H₂SO₄, ammonium tartrate, or the like. The container 52may also include a cylindrical mesh electrode 56, and the wire portion46 to be oxidized may be disposed through the center of the cylindricalmesh electrode 56. The mesh 56 and wire 46 may be coupled to acontrollable power source 58. Then, a current (direct, alternating, orpulsed) may be passed through the solution 54, creating an oxide layerabout the wire 46. This oxide layer further protects the wire againstcorrosion and imparts a conductive barrier to electrically isolate thewire from adjacent components and structures. The wire portions 46 ofmultiple bulbed wires 42 may be anodized at once. Although the entirestructure can be anodized, the preferred embodiment anodizes only theregions of the assembly that will be adjacent to other conductivestructures to provide an insulative barrier. For example, the wire 46and bulb 44 may be composed of tantalum, and only the wire 46 may thenbe anodized to create an oxide layer. This process may be used forcomponents of any of the distal assemblies shown and described hereinthat include an oxide layer.

Referring now to FIG. 5, a schematic diagram of a holder 60 adapted tocontain bulbed wires 42 for use in conjunction with a process forimparting further corrosion resistance to the bulbed wires 42 of FIG. 3is shown. After being anodized, one or more materials may be depositedon the bulbs 44 to enhance electrical conductivity, provide addedcorrosion resistance, or impart other beneficial qualities. For example,iridium oxide may be electrodeposited on the bulbs 44 or nickel-titaniumalloy may be sputtered onto the bulbs 44. Additionally or alternatively,sputtering may be used to deposit nickel-titanium alloy, gold, goldalloy, platinum or platinum-based alloy, or the like. However, othermaterials and techniques may be used. For example, the wire 42 may becomposed of gold with a tantalum coating. The tantalum coating on thebulb 44 may be etched, and the exposed gold may then be anodized orelectroplated, sputtered, or ion-embedded with a coating ofplatinum-iridium. Prior to treating the bulbs 44 (for example, byelectrodeposition or sputtering), one or more bulbed wires 42 may beplaced into a holder or container 60 to hold them in place. The holderor container 60 may be adapted to hold any number of wires 42, and maygenerally hold the wires 42 such that the bulbs 44 are accessible on thetop of the holder 60 (as shown in FIG. 3). Once the wires 42 are inplace, the bulbs 44 may be treated.

Referring now to FIGS. 6A and 6B, a second and third embodiment of adistal assembly 14 is shown. In both embodiments, the electrode head 32(the conductive portion) and the electrode wire 34 (the insulatedportion) are not only composed of the same material, but are alsocreated from a single piece of material (collectively referred to as an“electrode”). This may reduce manufacturing cost and complexity.Additionally, more than one electrode wires 34 may be used within acatheter body 18 without the need for including insulation materialbetween the wires.

In the embodiment shown in FIG. 6A, a plurality (for example, three)electrode wires 34 are disposed within a medical device, such as acatheter elongate body 18. Each wire 34 may be composed of a metal (forexample, tantalum or TaKS) and include an outer insulative oxide layer(for example, tantalum pentoxide). When low-frequency or DC voltageflows through the wire, the wire 34 will function as an insulatedconductor of energy. Therefore, no additional insulative material isrequired within the medical device to electrically insulate each wire 34from the others. This may not only increase the available space withinthe medical device for other components such as pull wires, push rods,etc., but may also decrease manufacturing cost and complexity. Each wire34 may extend through internal portion of the elongate body 18 for adistance, and then exit the wall of the elongate body 18 at an exitpoint 62. From the exit point 62, the wire 34 may then be disposed aboutan exterior distal portion in one or more coils 64, which may bereferred to as an electrode head 32. Unlike the wire 34, this externalcoiled portion 64 may not include an oxidative layer, and therefore maybe electrically conductive. Further, the coiled portion 64 may have ahydrophilic coating to reduce the likelihood of air collecting withinthe turns of the coils. The electrodes 30 may be made as shown anddescribed in FIGS. 3-5. Additionally, a housing or at least a portion ofa medical device (for example, an elongate body) may be overmolded ontothe electrodes to provide a seal at the exit point 62. The distal tip 66of the elongate body 18 may have an atraumatic rounded or bluntconfiguration to prevent injury to the patient during mapping and/orablation procedures.

The embodiment shown in FIG. 6B has substantially the same configurationas the embodiment shown and described in FIG. 6A, except that a hypotube68 instead of a wire may be used. Like the wire of the embodiment inFIG. 6A, the hypotube 68 may comprise an electrode 30 (conductiveportion) and a “wire” 34 (insulated portion); however, unlike theembodiment in FIG. 6A, the hypotube 68 may contain a volume of coolantor saline solution for cooling the electrode 30 portion of the hypotube68 during ablation procedures (for example, during RF ablation). Theconductive portions of both embodiments shown in FIGS. 6A and 6B may beused for mapping and/or ablation. The small diameter hypotube providesincreased local tissue contact pressure against the endocardium in anyorientation, providing reliable MAP recording capability.

Referring now to FIGS. 7A and 7B, a fourth and fifth embodiment of thedistal assembly 14 are shown. These embodiments include an electrode 30that has both mapping and ablation functionality. As shown in FIG. 7A,one or more electrodes 30 may be disposed about the distal portion 22 ofa medical device, such as the flexible, elongate body 18 of a catheter.Although FIG. 7A shows two electrodes 30, any number of electrodes 30may be used. Each electrode 30 may include a conductive region 70 and aregion that is selectively conductive 72. As described herein, theelectrode 30 may be composed of a highly conductive metal such as goldand may include a thin film coating of a metal such as tantalum, and theselectively conductive region 72 may include an outer oxide layer,whereas the conductive region 70 does not. The oxide layer may be anoxide of aluminum, tungsten, titanium, tantalum, hafnium, niobium,zirconium (and alloys thereof). The oxide layer in the case of tantalumpentoxide may be between approximately 10 nm and approximately 5000 nm,preferably approximately 100 nm to approximately 1000 nm. Further, theconductive region may have a layer of conductive material such as goldor gold alloy sputtered, ion-embedded, or electrodeposited on an outersurface. The conductive region 70 may have a smaller surface area thanthe selectively conductive region 72. As a non-limiting example, twoelectrodes 30 may be positioned on the device distal end such that theconductive regions 70 are each located on the distal end of theelectrode 30, and the electrodes 30 are spaced a distance apart by thematerial of the device (for example, a catheter elongate body), whichmaterial provides insulation between electrodes. Further, a fluid lumen74 may be disposed within the elongate body 18 that is in fluidcommunication with a source of saline or similar fluid for cooling theelectrodes 30. During use, measurement by the electrodes 30 of alow-frequency intracardiac electrogram or direct current voltage will beonly from the portions of the electrodes in the conductive region 70,whereas the selectively conductive region 72 is insulated by the oxidelayer and does not measure electrograms. As described above, smallerelectrodes 30 are less likely to corrode under high voltage and producemore accurate electrograms. Activating the electrodes 30 withhigh-frequency pulses or RF energy may cause the entire electrode 30,both conductive 70 and selectively conductive regions 72, to function asan ablation electrode having a larger footprint than that of theelectrode when the selectively conductive region 72 is insulated duringmapping procedures.

The embodiment shown in FIG. 7B generally functions in the same manneras the embodiment shown in FIG. 7A. FIG. 7B, however, shows twoelectrodes 30 radially arranged about the distal portion 22 of thedevice (although any number of electrodes may be used). That is, eachelectrode 30 may be substantially disposed within a discrete circularsector of the distal region 22 of the device, for example, an elongatebody 18. The fluid lumen 74 may define an opening 76 at the distal tip66 of the device, and the conductive region 70 of each electrode 30 maybe closest to the lumen opening 76 or distal tip 66 to facilitatemapping when the selectively conductive region 72 is insulated. When theselectively conductive region 72 is conductive, the entirety of eachelectrode 30 may function as an ablation electrode. In both FIGS. 7A and7B, the fluid lumen 74 containing saline or similar nontoxic fluid maybe open to the environment, and the saline may be allowed to exit thedevice into the patient's bloodstream through the lumen opening 76.Alternatively, the fluid lumen may be in communication with a source ofrefrigerant that is expanded to cool the electrodes 30, and that isrecovered by a vacuum after it is expanded in the distal portion 22 ofthe device proximate the electrodes 30.

Referring now to FIG. 8, a sixth embodiment of a distal assembly isshown. The distal assembly 14 may have a generally conical shape, butmay include one or more protruding electrode rings 78 (for example threeprotruding electrode rings 78 are shown in FIG. 8). The protrudingelectrode rings 78 may have rounded edges to prevent injury to thepatient. Between the protruding electrode rings 78 may be one or morerecessed insulated portions 80. The protruding electrode rings 78 andrecessed insulated portions 80 may be composed of the same material. Forexample, the protruding electrode rings 78 and recessed insulatedportions 80 may be composed of a metal (for example, tantalum), and therecessed insulated portions 80 may have an oxide layer (for example,tantalum pentoxide) or may have a coating of an electrically insulatingand thermally conductive material (for example, diamond-like carbon). Asa non-limiting example, the oxide layer or the layer of thermallyconductive material may be between approximately 10 nm to approximately5000 nm. The protruding electrode rings 78 may function as mappingelectrodes, and the protrusions may enhance contact and establish ahigher local pressure between the rings and tissue, thereby enhancingdepolarization of the tissue during mapping procedures and providingmore reliable and accurate mapping (for example, MAP) signal recording.Additionally, if the insulated portions 80 are composed of a selectivelyconductive material, both the protruding electrode rings 78 andinsulated portions 80 may also be capable of functioning as a single,larger ablation electrode. Alternatively, the insulated portions 80could be composed of a different material. Even though this may add tomanufacturing cost and complexity, the configuration of the distalassembly would still function to produce better mapping signals.

Referring now to FIGS. 9A-9C, a seventh, eighth, and ninth embodimentare shown. All three embodiments may include a coiled hypotube electrode68 disposed about the distal portion 22 of a medical device, such as anelongate body 18 of a mapping and/or ablation catheter. It will beunderstood that the drawings show only a single winding but additional,more proximal windings may be included in an ablation device. In suchembodiments, the proximal windings may be made selectively conductive asdescribed previously. The hypotube 68 in each embodiment may be in fluidcommunication with a source of saline or similar fluid (as described inFIGS. 7A and 7B), or with a cryogenic fluid, for cooling the hypotubeelectrode 68. The small diameter hypotube may provide increased localtissue contact pressure against the endocardium in any orientation,providing reliable MAP recording capability. The hypotube 68 may becoiled or wound around the distal portion 22 of the elongate body 18,the hypotube 68 winding at least approximately 360° about the distalportion 22 of the elongate body 18. Alternatively, the hypotube mayinclude a coil or winding 82 that is distal from the elongate body 18(as shown in FIGS. 9A-9C). Alternatively, the hypotube may includemultiple coils or windings 82 that are disposed about the distal portionof the elongate body or that are distal from the elongate body 18.Further, the hypotube 68 of each embodiment may be composed of a metal(for example, tantalum or stainless steel plated with gold or goldalloy) and include one or more alternating selectively conductiveregions 72 or more proximal hypotube windings (not shown), having anoxide layer (for example, tantalum pentoxide). As a non-limitingexample, the oxide layer may be between approximately 10 nm toapproximately 5000 nm, preferably approximately 100 nm to approximately1000 nm. The exposed (non-oxidized) conductive regions 70 may be smaller(that is, have less surface area) than the oxidized selectivelyconductive regions 72 to enhance signal quality during mapping whenrecording intracardiac electrograms. Finally, all embodiments mayinclude one or more thermocouples or thermisters 84 in contact with thehypotube 68 to monitor temperature of the hypotube 68.

The hypotube of FIG. 9A may include a coil 82 that has a substantiallysmooth circumference without any bumps, ridges, or textures. Conversely,the hypotube 68 of FIG. 9B may include a plurality of elements 86 thatare prominent from (or protrude from) a surface of the hypotube 68 tofurther enhance local small area contact pressure with tissue at thesite of contact with each of the prominent elements 86, thus enhancingMAP signal recording capability by increasing local pressure on thetissue under the prominent elements 86. Each prominent element 86 mayextend from a surface of the hypotube 68, for example, the outercircumference or perimeter of the hypotube. Although four prominentelements 86 are shown in FIG. 9A, it will be understood that any numberof prominent elements 86 may be used to enhance contact between thehypotube 68 and tissue of interest.

Likewise, the hypotube 68 of FIG. 9C may be bent to include one or moresubstantially angular bends 88. Each bend 88 may be prominent from (orprotrude from) the outer circumference of the hypotube 68, thus creatingprominent sites about the hypotube 68 to further enhance local smallarea contact pressure with tissue and improving MAP signal recordingcapability. Although FIG. 9C shows three protuberant bends 88, it willbe understood that any number of bends may be included to enhance MAPsignal recording capability when the device is positioned in most anyorientation against tissue of interest. Alternatively, the embodimentsshown in FIGS. 9A-9C may be made entirely with a conductive surface andwithout the selectively conductive areas.

Referring now to FIGS. 10A-10H, various configurations of a tenthembodiment of a distal assembly 14 are shown. The embodiment shown inFIGS. 10A-10H may have the general appearance of a catheter such as thePulmonary Vein Ablation Catheter (PVAC) sold by Ablation Frontiers(Medtronic Inc., Minneapolis, Minn.), which is an over-the-wire circularmapping and ablation catheter. The PVAC device may include a carrier arm90 bearing one or more electrodes, typically having either nine or tenelectrodes 30. Although FIGS. 10B-10H show and describe only twoelectrodes 30 on the carrier arm 90, the features of the describedelectrodes 30 will also apply to any other electrodes 30 included on thecarrier arm 90. The electrodes 30 may be conductive, and the carrier arm90 may be composed of a non-conductive material 91 (as shown in FIG.10A). Alternatively, the embodiments of FIGS. 10A-10H may not includeindividual electrodes, but rather a flexible curved carrier arm 90 thatis composed of a metal, such as gold, with an electrically insulated butthermally conductive coating (for example, diamond-like carbon) or witha selectively conductive coating (for example, gold with a thin filmcoating of tantalum that is oxidized to form tantalum pentoxide), withone or more alternating uncoated conductive regions 70. As anon-limiting example, the oxide layer may be between approximately 10 nmto approximately 5000 nm, preferably approximately 100 nm toapproximately 1000 nm. The exposed or uncoated conductive regions 70 maybe smaller (that is, have less surface area) than the oxidizedselectively conductive regions 72 (or electrically insulated butthermally conductive regions) to enhance signal quality during mappingwhen intracardiac electrogram voltage is measured. Alternatively, theconductive regions 70 and selectively conductive regions 72 may be thesame size. As a non-limiting example in which electrodes 30, are borneon the carrier arm 90, the carrier arm 90 may have a diameter ofapproximately 25 mm, and each of the electrodes 30 and portions of thecarrier arm 90 between the electrodes 30 may be approximately 3 mm wide.Further, the carrier arm 90 may include ten electrodes affixed thereto.

A first end 92 of the carrier arm 90 may be affixed to, for example, anelongate body 18 of the device, whereas a second end 94 of the carrierarm 90 may be affixed to a guidewire sheath 96 that is slidablyreceivable within the device. Therefore, the carrier arm 90 may betransitionable from a substantially linear delivery configuration whenthe guidewire sheath 96 is extended to a curved treatment configurationwhen the guidewire sheath 96 is retracted or partially retracted. Forexample, FIG. 10A shows the guidewire sheath 96 being partiallyretracted, and the carrier arm 90 extending approximately 360° betweenthe first end 92 and the second end 94 of the carrier arm 90.

FIG. 10B shows a close-up view of a portion of the carrier arm 90,wherein the conductive regions 70 are entirely conductive. The entirecarrier arm 90 may be non-conductive or selectively conductive in orderto ablate or electroporate tissue when high-frequency or pulsed currentis applied (for example, RF voltage). Alternatively, the carrier arm 90may be electrically insulated and thermally conductive, as described forFIGS. 10C-10H. Further, although FIG. 10B shows electrodes 30 affixed tothe carrier arm 90, the electrodes 30 may be integral to the carrier arm90, as described above in FIG. 10A. In the example shown in FIG. 10B,the conductive electrodes 30 are affixed to the carrier arm 90, and thecarrier arm 90 is selectively conductive 72. Further, the conductive 70electrodes 30 shown in FIG. 10B may wrap all the way around thecircumference of a cross section of the carrier arm 90. The figure alsoshows a portion of an electrogram signal (inset).

FIGS. 10C-10H show close-up views of carrier arm 90 portions wherein theelectrodes 30 are partially conductive. That is, the electrodes 30 areconductive only in certain areas, in particular, areas that will be incontact with target tissue (for example, an anterior or tissue-facingsurface 48 of the carrier arm 90). For example, the electrodes 30 may becomposed of a material, such as gold or gold alloy, that is affixed tothe outer surface of the carrier arm 90 (which may be non-conductive 91,selectively conductive 72, or electrically insulated but thermallyconductive 97; depicted in the figures as “92/72/97”), and only aportion of the electrode 30 may be uncoated or exposed (that is,conductive). The remaining portions 100 of the electrodes 30 may beselectively conductive (for example, composed of gold with a thin filmouter layer of tantalum that has been oxidized to form tantalumpentoxide) or electrically insulated but thermally conductive (forexample, having an outer layer of diamond-like carbon). The electricallyinsulative but thermally conductive layer may dissipate heat to thebloodstream yet prevent energy loss to the non-tissue-facing surfacesthat are not in tissue contact. The electrically insulative butthermally conductive layer may be a thin coating of one or morematerials such as thermal pyrolytic graphite, graphite, graphene,diamond, diamond-like carbon (DLC) coatings, alumina, sapphire,zirconia, tantala, titania, beryllium oxide, polymer compositescontaining thermally conductive particles, nanoparticles,self-assembling nanoparticles, nanomaterials and composites,biocompatible thermally conductive fluids like olive oil, medical gradesilicone oil, and similar materials. Further, this layer may be betweenapproximately 10 nm and approximately 5000 nm.

Alternatively, the electrodes 30 may be integral to the carrier arm 90,with the conductive regions 70 being exposed or not having an outeroxide layer or layer of electrically insulated but thermally conductivematerial (for example, diamond-like carbon). In either configuration,the non-tissue-facing surfaces of both the electrode 30 and the carrierarm 90 (for example, if the carrier arm 90 is selectively conductive)may include an electrically isolated but thermally conductive layer,with only the anterior or tissue-facing surfaces of the electrodes 30being conductive. Further, in all embodiments, the conductive regions 70may be smaller than the non-conductive or selectively conductiveportions, or they may be the same size. None of the figures shown hereinmay be drawn to scale. FIGS. 10C-10H also show a portion of an enhancedelectrogram signal (inset) that may be achieved using the devices ofFIGS. 10C-10H.

In FIGS. 10C-10E, the conductive regions 70 of the electrodes 30 may belinear. In FIGS. 10E-10H, the conductive regions 70 may be substantiallycircular. In FIGS. 10G and 10H, the circular conductive regions 70 maybe raised or may protrude from the surface of the carrier arm 90 in aprominent bump 102. As discussed in FIGS. 9B and 9C, this prominent bump102 may further enhance electrogram signal quality. Further, when veryminimal or open signal filtering is applied (for example, approximately0.5 Hz to approximately 1000 Hz), the prominent bump 102 may produce amonophasic action potential when referenced against a non-tissue-facingreference electrode 24, as shown in FIG. 10H. The reference electrode 24may be located on the distal portion of the elongate body 17 (as shownin FIG. 10A) or on a non-tissue-facing surface of the carrier arm 90(not shown).

Referring now to FIG. 11, an eleventh embodiment of a distal assembly isshown. The device may be a focal catheter having a rounded distal tip66. A mapping and ablation electrode 30 may be disposed over the distaltip 66 and portion of the distal portion 22 of the elongate body 18, asshown. The electrode 30 may include a conductive region 70 and anon-conductive or selectively conductive region 104. In oneconfiguration, the region 104 may be selectively conductive. Both theconductive 70 and selectively conductive 104 regions may be composed ofa metal such as gold or gold alloy, and the selectively conductiveregion 104 may, for example, have a thin film layer of tantalum over thegold and the tantalum layer may be oxidized to tantalum pentoxide. As anon-limiting example, the oxide layer may be between approximately 10 nmto approximately 5000 nm, preferably approximately 100 nm toapproximately 1000 nm. In this case, the conductive region 70 may beused for mapping procedures and the entire electrode 30 may be used forablation or electroporation procedures (as described in more detail in,for example, FIG. 2). In another configuration, the region 104 may benon-conductive. The entire electrode 30 may be composed of a conductivemetal (for example, gold or gold alloys), but the non-conductive region104 may have a coating with a material that is highly thermallyconductive but is fully electrically insulative, such as thermalpyrolytic graphite, graphite, graphene, diamond, diamond-like carbon(DLC) coatings, alumina, sapphire, zirconia, tantala, titania, berylliumoxide, polymer composites containing thermally conductive particles,nanoparticles, self-assembling nanoparticles, nanomaterials andcomposites, biocompatible thermally conductive fluids like olive oil,medical grade silicone oil, and similar materials. In this case, thedevice may provide enhanced electrogram signal quality (due to thesmaller region of the electrode 30 that is used for mapping proceduresand the interference-mitigating effect of the coating), a high coolingcapability, and a reduced loss of ablation or electroporation energy tothe bloodstream.

Referring now to FIGS. 12A and 12B, a twelfth embodiment of a distalassembly is shown. The distal assembly 14 may include one or morecarrier arms 106 bearing one or more mapping and/or ablation electrodes30. One carrier arm 106 is shown in FIG. 12A for simplicity; however,two or more carrier arms 106 may be used. For example, FIG. 12B showsthe anterior or tissue-facing surface 48 of distal assembly 14 includingtwo carrier arms 106. Each carrier arm 106 may include a first portion108 at the anterior or tissue-facing surface 48 of the carrier arm 106on which the one or more mapping and/or ablation electrodes 30 areborne, and two second portions 110 that are coupled to the device 12.The distal assembly 14 may further include one or more referenceelectrodes 24. Each of the electrodes 30 may include a conductive region70 and a region that is electrically insulated but highly thermallyconductive 97. For example, both the conductive region 70 and theinsulated region 97 may be composed of gold or gold alloy, whereas theinsulated region 97 may include a thin film coating or layer ofdiamond-like carbon (DLC). Although not shown in FIG. 12A or 12B, theelectrode 30 may be composed of gold with a thin film surface oftantalum, and may include selectively conductive regions 72 in which thetantalum layer is oxidized to form tantalum pentoxide. These selectivelyconductive regions 72 may largely correspond to the insulated regions 97shown in FIGS. 12A and 12B. As a non-limiting example, the oxide layermay be between approximately 10 nm to approximately 5000 nm, preferablyapproximately 100 nm to approximately 1000 nm. The point at which thefirst 108 and second 110 portion of each carrier arm 106 meet may forman acute angle. The second portion 110 of each arm 106 may be affixed toa shaft that is slidably movable within the elongate body 16 of thedevice 12, or affixed directly to the elongate body 18. Further, thedistal assembly 14 may be composed of a resilient and deformablematerial, and may assume a first position for delivery (not shown) and asecond position for mapping and/or treatment (as shown in FIG. 12A).When in the second expanded position, the first portion 108 of each arm106 may lie in a plane that is substantially orthogonal to thelongitudinal axis of the device 12. Still further, the resilient anddeformable material may be biased toward either the first or secondposition and may be steerable by one or more pull wires, guide wires,rods, or other steering mechanisms controllable at or proximal to thehandle 28 of the device 12. The one or more electrodes 30 may be capableof transmitting both low-frequency and high-frequency current, and maybe suited for mapping, ablation, and/or electroporation.

The embodiments shown and described in FIGS. 10 and 12, in particular,may be suited for anatomical placement, such that certain areas of theelectrode 30 will be tissue contacting while other areas will only be incontact with the blood. The Medtronic Ablation Frontiers Pulmonary VeinAblation Catheter® (PVAC) is an example of such a device as shown anddescribed in FIGS. 10A-10H, and the Medtronic Ablation FrontiersMulti-Array Ablation Catheter® (MAAC) is an example of such a device asshown and described in FIGS. 12A and 12B. The exposed fully electricallyconductive regions 70 of the electrodes 30 are specifically placed inareas of the electrode 30 that will contact cardiac muscle that is to beelectrically mapped and potentially ablated. In some embodiments, thenon-cardiac muscle facing portions of the electrode 30 may be coatedwith the electrically insulative material that is also highly thermallyconductive. Two important functions are served by the coating: duringmapping, the non-cardiac muscle (tissue) facing surfaces do not collectfar-field electrical signals that degrade quality of local electrograms;and, during ablation (for example, RF ablation) or electroporation, thenon-muscle facing surfaces do not waste energy to the blood but thesesurfaces serve to dissipate heat collected by the tissue facing side ofthe electrode, through the electrode and into the flowing blood.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention, which is limited only by the following claims.

What is claimed is:
 1. A medical device comprising: an elongate bodyhaving an external surface; and a metal electrode having a proximalportion, a distal portion, and an external surface, at least a portionof the proximal portion of the electrode being disposed within theelongate body and at least a portion of the distal portion of theelectrode being disposed about the external surface of the elongatebody.
 2. The medical device of claim 1, wherein the metal is selectedfrom the group consisting of platinum, platinum alloys, gold, goldalloys, gold with a coating of tantalum, copper with a coating oftantalum, copper with a coating of gold, aluminum, tungsten, titanium,tantalum, hafnium, niobium, zirconium, and combinations thereof.
 3. Themedical device of claim 2, wherein the portion of the electrode disposedwithin the elongate body includes a substantially insulative layer. 4.The medical device of claim 3, wherein the substantially insulativelayer is a layer of oxidized metal from the group consisting ofaluminum, tungsten, titanium, tantalum, hafnium, niobium, zirconium, andalloys thereof.
 5. The medical device of claim 4, wherein the distalportion of the electrode is coiled about the external surface of atleast a portion of the distal portion of the elongate body.
 6. Themedical device of claim 5, further comprising two or more electrodes. 7.The medical device of claim 6, wherein the coiled portion of the distalportion of the electrode includes at least two coils of approximately360° each.
 8. The medical device of claim 6, wherein the electrode is atantalum wire.
 9. The medical device of claim 6, wherein the electrodeis a hypotube electrode.
 10. The medical device of claim 9, wherein thehypotube electrode includes a lumen extending between the distal portionand proximal portion of the hypotube electrode.
 11. The medical deviceof claim 10, further including a fluid within the lumen that is inthermal exchange with the external surface of the hypotube electrode.12. The medical device of claim 11, wherein the fluid is a salinesolution.
 13. A medical device, comprising: an elongate body having anexternal surface, a proximal portion, and a distal portion; and aplurality of electrodes composed of a tantalum and having an insulatedproximal portion, a conductive distal portion, and an external surface,at least a portion of the proximal portion of each of the plurality ofelectrodes being disposed within the elongate body and having aninsulative oxidized layer, and a distal portion of each of the pluralityof electrodes being coiled about the external surface of at least aportion of the distal portion of the elongate body.
 14. The medicaldevice of claim 13, wherein the plurality of electrodes are hypotubeelectrodes.
 15. A medical device distal assembly comprising: a distalassembly housing element having a longitudinal axis and an externalsurface, the distal assembly housing element being composed of aconductive material having a substantially insulative layer on theexternal surface; and a plurality of electrodes coupled to the distalassembly housing element, the plurality of electrodes being composed ofa conductive material and substantially having a radial symmetry aboutthe housing element longitudinal axis, each of the plurality ofelectrodes including an integrated electrode head and electrode wire,each electrode wire having an external surface and a substantiallyinsulative layer on the external surface.
 16. The distal assembly ofclaim 19, wherein the conductive material selected from the groupconsisting of metals, doped semiconductors, conductive polymers, metalpolymers, and metal-ceramic composites.
 17. The distal assembly of claim20, wherein the conductive material is a metal from the group consistingof platinum, platinum alloys, gold, gold alloys, gold with a coating oftantalum, copper, copper with a coating of tantalum, copper with acoating of gold, aluminum, tungsten, titanium, tantalum, hafnium,niobium, zirconium, and combinations thereof, and the substantiallyinsulative layer is pyrolytic graphite, graphite, graphene, diamond,diamond-like carbon (DLC) coating, alumina, sapphire, zirconia, tantala,titania, beryllium oxide, polymer composites containing thermallyconductive particles, nanoparticles, self-assembling nanoparticles,nanomaterials and composites, olive oil, medical grade silicone oil, orcombinations thereof.
 18. The distal assembly of claim 21, wherein theconductive material is tantalum and the substantially insulative layeris tantalum pentoxide.
 19. A medical system comprising: a radiofrequencyenergy source; a distal assembly housing element having a longitudinalaxis, the distal assembly housing element being composed of a conductivematerial and being in electrical communication with the radiofrequencyenergy source; and a plurality of electrodes coupled to the distalassembly housing element and in electrical communication with theradiofrequency energy source, the plurality of electrodes being composedof a conductive material and substantially having a radial symmetryabout the housing element longitudinal axis, each of the plurality ofelectrodes including an integrated electrode head and electrode wire,each electrode wire having an external surface and a substantiallyinsulative layer on the external surface.
 20. The system of claim 23,wherein a substantially insulative layer is disposed between the distalassembly housing element and the plurality of electrodes, such that thedistal assembly housing element and plurality of electrodes areelectrically isolated from each other.